1. Field of the invention
The present invention relates to a magnetic material which is suitable for use in magnetic cores for electronic equipment such as transformer cores or magnetic heads, as well as permanent magnets.
2. Description of the Prior Art
In cases where high magnetic flux density is required, magnetic metals are used as magnetic materials for electronic components, electronic equipment and other products. However, owing to large eddy current losses, magnetic metals cannot be used in the high frequency regions, and therefore, in place of the magnetic metals that is a low electrical resistance material, high electrical resistance ferrites are used.
The aforementioned ferrites are metal oxides having magnetic properties with electrical resistivities more then 10,000 times greater than those of magnetic metals, and are therefore vastly superior to magnetic metals insofar as their eddy current losses are far lower. However, a shortcoming of ferrites consists in the fact that their saturation magnetization flux density is about 1/2 or less than that of magnetic metals, which renders ferrites unsuitable for use in electronic components or equipment requiring particularly high saturation magnetization flux density.
Certain composites of magnetic metals and electrical insulators have been developed as magnetic materials with high electrical resistivity and low eddy current losses even in high frequency regions. Such composites are prepared, for example, from a magnetic metal powder and a ceramic powder by mixing, molding and sintering. However, as shown in FIG. 9, the composites so obtained comprise magnetic metal granules 101 dispersed in an insulating phase 102, and the said granules are mutually separated by distances varying from several microns to several tens of microns. Therefore, the magnetic flux penetrating the interior of this composite material is blocked by the insulating substance, and consequently the magnetic permeability is markedly reduced. Thus, conventional composites of magnetic metals and insulators cannot possess characteristics other than those merely representing averages of the corresponding properties of the constituent substances. Consequently, if the proportion of the insulating substance is increased in order to obtain high electrical resistivity, then the magnetic flux density is reduced. This makes it impossible to attain the high magnetic flux density which is obtainable when only magnetic metals are used.
In addition to the aforementioned dispersed type of magnetic material, for example, laminated materials composed of alternating thin layers of metal and a dielectric substance are also known. However, processes for manufacturing this type of magnetic material are complex and therefore entail high costs. Moreover, the stress applied in the lamination process gives rise to plastic deformation, thereby disrupting the thin laminar structure, which may adversely affect the desired magnetic characteristics of the material. These shortcomings indicate the need for magnetic materials which, in bulk form, possesses performance characteristics equivalent to those of such laminated materials.